The invention relates to a board cutter for cutting gypsum board and foam insulation board and more particularly to a combination T-square guide and mat knife for accurately cutting large boards.
Builders employ gypsum board for interior walls and ceilings and foam insulation board for insulation coverings of various surfaces in home and commercial building construction. These boards are generally about four feet wide and eight, twelve or sixteen feet long. The dimensions vary somewhat if the sheets are metric. The boards are cut for attachment to wall studs and other structural beams.
The cuts in gypsum board and foam insulation board must be fairly accurate to fit on the studs and to provide good joints between boards. The cuts must also be made quickly to reduce building costs. Both gypsum board and foam insulation boards are severed by making a shallow cut and then breaking the boards along a line where the boards are weakened by the shallow cut.
Cuts across the width of a board are made quickly and accurately using a T-square with a long leg that is up to four feet long and a mat knife. A four-foot T-square is easily transported without damage.
Making a straight cut that extends the length of gypsum and foam insulation boards is relatively difficult. Transportation of long beams with a straight edge is also difficult. Frequently long straight edge members are bent and destroyed. Long beams with a straight edge may require an additional person to hold the straight edge beam during cutting with a mat knife.
Long cuts have been made by construction workers using a T-square and a knifeblade. Numerous T-square and knife combinations have been tried over the years. These combination T-squares and knifeblades have drawbacks that result from having a knifeblade that is rigidly secured to the long leg of the T-square. The knifeblade tends to raise the long leg up off of the surface of the board that is being cut when hard material spots in the board are encountered. Up and down movement of the long leg of the T-square makes it somewhat more difficult to accurately guide the knifeblade and cut the board along a straight line occasionally construction workers like to make a second deeper cut when hard material is encountered in a board. To increase the depth of a knifeblade that is rigidly clamped to a T-square, it is necessary to loosen the blade, reset the position of the blade and then clamp the blade back to the blade holder. This procedure takes time. It can also be difficult to determine a depth setting of the blade.
Knifeblade penetration forces and cutting forces are transmitted between the knifeblade and the long leg of a T-square when the knifeblade is rigidly secured to the T-square. The T-square must be somewhat stronger and weigh more to withstand these extra forces. The transmission of force through the T-square to the knifeblade to obtain penetration and to cut material makes guidance of the blade by the T-square somewhat more difficult and less accurate.
The combination T-square and mat knife cutter for making straight cuts in long sheets of gypsum board and foam insulation boards includes a head with a board edge contact surface and a board face contact surface. A long leg is connected to the head. A bottom surface of the long leg is a board face contact surface that slides along the face surface of a board that is being cut. A slider is slideably mounted on an upper surface of the long leg. A clamp fixes the position of the slider in selected positions along the length of the long leg. A knife having a handle and a knifeblade is pivotally connected to a knife support on the slider for pivotal movement about a knife axis. The knife axis is parallel to a long axis of the long leg of the T-square and spaced from the board face contact surface.
The connection of the knife to the T-square for pivotal movement about a knife axis allows a construction worker and others to manually control the depth of cut and the pressure exerted on the knifeblade. The T-square guides the knifeblade only. A board face contact surface on the long leg can remain in sliding contact with a board that is being cut. Forces exerted on the T-square by the mat knife during cutting are minimized. Reducing the force exerted on the T-square permits a reduction in T-square weight and improves the accuracy of a cut in a board at the same time. If the construction worker wishes to make a second deeper cut in the same location, the T-square and mat knife are moved back to the starting position and another cut is made. No additional adjustment is required.